Standard noise source



July 4, 1967 STANDARD NOISE SOURCE Filed June 1, 1966 5 Sheets-Sheet 1 INVENTOR HANNO HERWART HELLER ZU 1M ATTORNEY July 4, 1967 H. H. HELLER 3,329,234

STANDARD NOISE SOURCE Filed June 1, 1966 5 Sheets-Sheet 2 FlG.2d.

FIG.40

Sound pressure level per octave in db re 2 l0'4 )1!) (0 O O 0.025 0.05 O.l 0.2 0.4 0.8 L6 32 6.3 I25 25 kc/s I30 Sound pressure level per oclave in db re 2l0 J-Ib .025 0.05 O.| 02 0.4 0.8 L6 3.2 6.3 I25 25 kc/s 4b INVENTOR HANNO HERWART HELLER ATTORNEY July 4, 1967 H. H. HELLER STANDARD NOISE SOURCE 3 Sheets-Sheet 3 Filed June 1, 1966 INVENTOR FIG. 3.

HANNO HERWART HELLER BY;

ATTORNEY United States Patent 3,329,234 STANDARD NOISE SOURCE Hanno Herwart Heller, 2 Eggepfad, 1 Berlin 37, Germany Filed June 1, 1966, Ser. No. 554,953 5 Claims. (Cl. 181-.5)

ABSTRACT OF THE DISCLOSURE An apparatus for producing sound having a ball fling sound source and a damped plate sound source which in combination produce a. sound covering a wide frequency range with a constant relative band width.

The present invention relates to a standard noise source and more particularly to a combination of ball fling and damped plate noise sources to provide a noise source with a constant sound output per constant relative band width.

It has been difficult to construct one single sound source which could cover a wide frequency range of nearly seven octaves with a sound output as constant as possible per constant relative band width. To obtain a noise source with a constant sound output per constant relative band width, that is, 100 db per octave in the frequency range from 100 to 10,000 c.p.s., electro-acoustic equipment could be used. Since this equipment would require expensive generators, amplifiers, and voluminous loudspeakers, it would be more economical to construct a purely mechanical noise source.

Early experiments were made with aerodynamic sound, that is, the sound radiation of air jets. These jets, although having a high sound output, especially in the high frequency range, had many disadvantages. To obtain such jets, it was necessary to use a compressor, a calming tank and a pressure control or a jet speed control. To generate sound levels which are high enough, the jet must have a high speed, and cannot be too small in diameter, resulting in a large consumption of air.

Another possibility to produce high sound levels was to use small diesel combustion engines. These motors, although producing a loud noise, do so only in a very narrow frequency range. Other problems involved were that they were inconvenient to operate because of noxious fumes and because there was a problem of speed control.

Because of the prior art disadvantages it-was important to design a noise source which is convenient to handle, clean and robust, and driven by a readily accessible source of power.

An object of this invention is to provide a standard noise source with a constant sound output per constant relative band width.

Another object is to provide a standard noise source with a constant sound output of 100' db per octave in the frequency range from 100 to 10,000 c.p.s.

A further object is to provide a standard noise source with novel means for vibrating or stimulating a sounding board.

A still further object is to combine a low frequency sound source and a high frequency sound source to obtain a broad band standard noise source.

Another object is to provide a sound source of improved construction, increased utility, durability and efiiciency.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings in which:

FIGURE 1 is a side view partly in section of a standard noise source.

FIGURES 2a and 2b are side schematic views of a low frequency noise source.

FIGURE 3 is a side view, in section, of a high frequency noise source.

FIGURES 4a and 4b show graphs of the output of a standard noise source.

The invention consists primarily of two parts, one for low frequencies and the other for the high frequency part of the spectrum. Each part operates on the same principle, that is, a specially formed plate is stimulated or vibrated by shocks.

To produce a low frequency sound of suflicient energy there must be a large area vibrating with large amplitudes. A suitable material which can be used is Novopan, a material consisting of wood shavings, pressed and cemented to form a flat sheet similar to plywood. The vibrating material is stimulated by a specially constructed hammer machine.

The high frequency sound source operates on a similar principle whereby a material is stimulated by small balls. In the high frequency sound source, the balls are flung against a sounding board by centrifugal action with high force. The sounding board may be a hollow hemisphere of steel or hard plastic or any sound damping material. The selection of the type of material to use as a sounding board will depend on the desired spectrum. Combining the high and low frequency noise sources into one unit, provides a standard noise source.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIGURE 1, a standard noise source. The invention comprises primarily a low frequency noise source 11 and a high frequency noise source 22.

FIGURE 1 shows a principle sketch of the low frequency noise source 11. A disk 12, fixed on a shaft 13, is driven by an electric motor 14 and is rotated at a high speed. Near to the edge of this disk 12 are two bolts 15 of high quality steel located opposite to each other and projecting parallel with the axis of the disk 12, each of the bolts 15 are provided with an enlarged section 16.

Annular disks 17, have a central opening substantially larger than the diameter of the bolts 15 upon which they are pivoted, but smaller than the enlarged section 16. The annular disks 17, which are suspended relatively loose, can move in a radial direction on the bolts 15, restricted by the greater diameter of the enlarged section 16. When the disk 12 is rotated with high speed, the annular disks 17 are hurled in an outwardly direction by centrifugal force.

Mounted directly above the disk 12 is a sounding board 18 having a plate of wear resistant plastic 19 mounted thereon in such a manner as to transmit the impact force from the annular disks 17 to the sounding board 18. The sounding board 18 is fixed at an appropriate distance above the disk 12 to enable the annular disks 17 to contact the sounding board 18, the force of the contact being dependent on the distance of the sounding board 18 from the shaft 13.

FIGURE 2a shows the annular disk 17 as it initially contacts the sounding board 18 and FIGURE 2b shows the disk 12 and the annular disks 17 in their topmost position. In this embodiment, with an rpm. of 1500, the sounding board is stimulated times per' second.

The sounding board 18 must also be allowed to vibrate. To meet this objective, the sounding board 18 must not be firmly fixed to the box 18a. To accomplish this purpose, a bolt and spring arrangement, not shown in the drawings, may be used. This means of attaching the sounding board 18 to the box 18a, first allows the sounding board 18 to vibrate, and second makes it possible to Patented July 4, 1967- 3 adjust the distance between the sounding board 18 and the disk 12, thereby regulating the intensity of the sound output. The plate 19 protects the sounding board 18 from excessive Wear caused by the pounding of annular disks 17 The principle of operation of the high frequency noise source 22 is similar to that of the low frequency noise source 11. Small balls 23 are rotated in a bowl 24 until centrifugal force hurls them upward and out of the bowl toward a sounding board 25. The sounding board 25 and the balls 23 may be fabricated from various available materials, depending upon the intensity and frequency range desired. If a steel cylindrical shaped sounding board is selected, a rather sharp peak in the spectrum is obtained. When a plastic cylinder, such as Pertinax, is used, the peak is flattened, which of course provides a better standard noise source. The sounding board 25 as well as sounding board 18 of the low frequency noise source could either be flat or curved.

In a preferred embodiment, FIG. 3, the balls 23 are fabricated from steel and are approximately mm. diameter. An electric motor 14 of 150 watts, shown in the drawings, is suspended vertically on a metal plate. Fixed on the shaft of this motor is a fling bowl 24. The bowl 24 contains radial grooves 26, which lead and accelerate the balls 23 when the bowl 24 is rotated. The balls 23 then are hurled out of the bowl 24 oblique upwards and impact against sounding board 25 at a high rate of speed, thus stimulating the sounding board 25. After hitting the sounding board 25, the balls 23 fall back into bowl 24 and the process repeats. Thus a very intense and continuous noise will be produced. The flat c-one 27 in the bottom center of the bowl 24 is required to lead the balls 23 out of the center of the bowl 24 to give them an initial centrifugal force and thus enabling them to ascend on the wall of the bowl 24. To prevent the balls 23 from flying out of the cylinder, a cover 28 is fixed on the upper end.

To receive a uniform sound field, the high frequency noise source 22 is placed on top of the low frequency noise source 11. For acoustic measurements, a condenser microphone 1 m. above ground and in four different positions around the standard noise source in 1 m. distance from the enter axis was used. The results show that there is no pronounced directivity, although the sound pressure level of the low frequency noise source 11 fluctuates about :3 db. The sound pressure level of the high frequency noise source 22 fluctuates about db.

The low frequency noise source 11 has its maximum sound output from 100 to 800 cycles per second and the high frequency noise source 22 has its maximum output in the frequency range 3.2 to 12.5 kilocycles per second. Both sources reached the desired 100 db/ octave.

When the standard noise source is in operation the results obtained are as shown by the graphs in FIGS. 4a and 4b. FIG. 4a shows both spectra, i.e. the low frequency and the high frequency. FIG. 4b shows the total spectrum of the standard noise source. It is evident that the sound pressure level is close to 100 db per octave from 100 to 12,500 c./s. In the frequency range, where the two spectra intersect, there is a hole, i.e., the octave band of the mid frequency 1600 c./s. shows only 93 db. It is possible to lift the sound output in this octave band by changing the construction of the high frequency noise source, e.g. by enlarging the diameter of the sounding board 25 in order to lower the spectrum to lower frequencies.

The standard noise source of this invention is rather large. The volume of the box 18a of the low frequency noise source 11 cannot be reduced, since low frequencies need large plates to vibrate and not too small boxes behind. By minor changes of construction the invention may be built more compact and with less weight, but still having the same acoustical qualities.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A broad band sound source comprising:

means for producing a low frequency sound of a substantially wide frequency range and a substantially constant sound level,

a resonance chamber in the form of a sounding box of particular dimensions, said dimensions being determined by size limitations of the desired frequency range and intensity, and

means for producing a high frequency sound of a substantially wide frequency range and a substantially constant sound level,

said sound producing means being mounted in substantially close proximity to each other on opposite sides of said resonance chamber and in combination with said resonance chamber producing a high intensity sound having a wide frequency range and a constant sound output per constant relative band width.

2. A broad band sound source according to claim 1, wherein said means for producing a low frequency sound comprises:

a base, a motor mounted on said base,

a sounding board capable of absorbing heavy impacts and vibrating at a predetermined range of frequencies,

a rapidly rotatable disk adapted to be rotated by said motor and provided with at least one annular disk pivoted thereon for striking said sounding board.

3. A broad band sound source according to claim 1, wherein said means for producing a high frequency sound comprises:

a base, a motor mounted on said base,

a sounding board capable of absorbing heavy impacts and vibrating at a predetermined range of frequencies,

a rotatable bowl adapted to be rotated by said motor and having a plurality of projectile feeding passages therein, and

a plurality of projectiles for impacting said sounding board.

4. A standard noise source of the type which combines the outputs of a low frequency noise source and a high frequency noise source to obtain a constant level output comprising:

a first and second sounding board, each capable of absorbing heavy impacts and capable of vibrating at a predetermined range of frequencies,

a first rotary vibrator including a motor and embodying therein a rotatable disk adapted to be rotated by said motor and with at least one annular disk pivoted thereon for striking said first sounding board, said annular disks mounted as to have a limited radial movement,

a second rotary vibrator including a motor and embodying therein a rotatable bowl adapted to be rotated by said motor and having a plurality of radial projectile feeding passages and containing a plurality of projectiles in the form of balls capable of being continuously cycled between said rotatable bowl and said second sounding board,

a resonance chamber in the form of a sounding box of particular dimensions, said dimensions determined by size limitations of the desired frequency range,

said first and second rotary vibrators and sounding boards being mounted in substantially close proximity to each other on opposite sides of said resonance chamber and in combination with said resonance chamber producing a localized constant sound output.

5. A high frequency noise source of the rotary vibratory type comprising:

a base, a motor mounted on said base,

a plurality of projectiles in the form of balls, the size and material of said projectile dependent upon the desired sound spectrum,

a bowl adapted to be rotated by said motor and having a plurality of projectile feeding radial grooves and a cone shaped inner surface for directing said projectiles radially into said grooves,

a sounding board placed in a position to encircle said bowl and to absorb the impact of said projectiles as they are hurled out of said bowl thereby being stimulated into vibration in a frequency range which is dependent upon a selection of material and shape.

References Cited UNITED STATES PATENTS SAMUEL FEINBERG, Primary Examiner.

BENJAMIN A. BORCHELT, Examiner.

M. F HUBLER, Assistant Examiner. 

1. A BROAD BAND SOUND SOURCE COMPRISING: MEANS FOR PRODUCING A LOW FREQUENCY SOUND OF SUBSTANTIALLY WIDE FREQUENCY RANGE AND A SUBSTANTIALLY CONSTANT SOUND LEVEL, A RESONANCE CHAMBER IN THE FORM OF A SOUNDING BOX OF PARTICULAR DIMENSIONS, SAID DIMENSIONS BEING DETERMINED BY SIZE LIMITATIONS OF THE DESIRED FREQUENCY RANGE AND INTENSITY, AND MEANS FOR PRODUCING A HIGH FREQUENCY SOUND OF A SUBSTANTIALLY WIDE FREQUENCY RANGE AND A SUBSTANTIALLY CONSTANT SOUND LEVEL, SAID SOUND PRODUCING MEANS BEING MOUNTED IN SUBSTANTIALLY CLOSE PROXIMITY TO EACH OTHER ON OPPOSITE SIDES OF SAID RESONANCE CHAMBER AND IN COMBINATION WITH SAID RESONANCE CHAMBER PRODUCING A HIGH INTENSITY SOUND HAVING A WIDE FREQUENCY RANGE AND A CONSTANT SOUND OUTPUT PER CONSTANT RELATIVE BAND WIDTH. 